Optical and thermal reducing of photochromic effect in Al doped Bi₁₂SiO₂₀ crystals

Abstract

Results of experimental studying the processes of reversible optical and thermal reducing of the photochromic effect in Bi₁₂SiO₂₀:Al crystals are presented. It is shown that the optical reducing is the most effective in the region hν = 0.5 - 2 eV and at hν > 1.4 eV the reducing process passes to excitation of the photochromic effect. The thermal reducing is held in two steps with the ultimate bleaching at Th = 152 and 208 K. It is suggested the model of electron transitions such as impurity level - band , where nonstoichiometric ions Bi⁵⁺Si (donors) and ions Al³⁺Si (acceptors) are responsible for impurity levels. Besides intracenter transitions in complexes [AlSiO₄] make a contribution to the processes of exiting and reducing of the photochromic effect.